Filtering apparatus for separating suspended matter from a liquid suspension having a movable filter media is a well known art as exemplified by U.S. Pat. Nos. 3,087,620 and 3,091,336.
The filtering apparatus generally includes a tank for receiving the liquid suspension containing suspended matters. A filtrate compartment is located contiguous to the tank for receiving the clean filtrate. A filter grid supporting a filter media is disposed between the tank and the filtrate compartment so as to permit passage of the filtrate but cause the suspended matter to collect and be deposited on the filter media. A conveyor system is intermittently activated to transport the filter media and the suspended matter deposited thereon up a ramp like end wall of the tank for disposal. A filtrate pump is used to withdraw the filtrate from the filtrates chamber. The pump has an additional function of recirculating clean filtrate back to the tooling machine and induces greater efficiency in the liquid solid separation by continuously removing the clean liquid filtrate from the filtrate compartment causing said compartment to be at a lower pressure than the tank thereby increasing the flow rate across the filter media.
As a result of the pressure differential between the tank and the filtrate compartment, a large force is imposed on the filter media so as to render movement of the filter media by the conveyor difficult. To overcome this difficulty, a reservoir containing a volume of clean filtrate, selectively filled by the filtrate pump, is operatively connected to the filtrate compartment. When the need to advance the filter media arises, the flow valve in a conduit connecting the reservoir to the compartment is opened to allow clean filtrate from the reservoir to neutralize the pressure differential between the filtrate compartment and the tank. This will eliminate the additional force on the filter media so that the conveyor system is effective to advance the filter media including the accumulatable suspended matter for disposal.
Filtering apparatus of the type described above is generally installed in a pit below the floor level. This arrangement is advantageous because trenches can be installed in the floor around the tooling machines that lead directly into the filtering tank. The filtrate which may be a coolant or cutting oil may therefore flow under gravity in the trenches to the tank.
Heretofore, the filtrate pump of an end suction centrifugal construction has been installed at the bottom of the pit and connected directly to the filtrate compartment. In the event of a breakdown, access to the pump located in the pit is awkward so that maintenance of the pump is difficult.
The filtrate pump may also be mounted on the floor level and connected to the suction end of the filtrate compartment in the pit. In this arrangement the pump is located above the liquid level in the filtrate compartment so that a self priming pump has been used in order to achieve proper start-up of the pumping and filtration operation. The self-priming pump is more expensive and less efficient than an end suction centrifugal pump as described in the previous arrangement.
Another known arrangement provides a vertical turbine pump having the impeller section which is located in the pit adjacent to the filtrate compartment and the motor extending vertically above the impeller. Vertical turbine pumps are expensive and require a hoist to assist in removing the pump from the pit when maintenance is required thereby adding more costs to the arrangement. It should be pointed out that all of the prior art arrangements provide a pressure relief conduit, regulated by an automatic vacuum break valve, connecting the reservoir to the filtrate compartment.
By the present invention, it is proposed to provide an end suction centrifugal filtrate pump arrangement which overcomes the difficulties encountered heretofore.
This is accomplished generally by a non self-priming pump located substantially on the same level as the floor level and below the level of the filtrate in the reservoir. Conduit means connect the filtrate compartment, the suction end of the pump and the filtrate reservoir. Valve means are disposed in the conduit means to permit reversal of flow of the filtrate in the latter. The hydraulic pressure of the reservoir maintains a positive liquid pressure at the suction end of the pump when the reservoir discharge valve is open thereby eliminating the need for a self-priming feature pump. The pump draws filtrate from the filtrate compartment with the reservoir discharge valve closed to prevent filtrate flowing out of the reservoir. The reservoir discharge valve is selectively opened to allow filtrate from reservoir to flow into the pump and the filtrate compartment neutralizing the pressure differential therein.